A. Field of the Invention
The present invention relates to a color former composition which comprises a mixture of defined color formers. The present invention further relates to micro-capsules containing the color former composition.
B. Description of the Related Art
Color formers are an essential ingredient for various types of recording material. Recording materials that contain both microcapsules containing colorless color former dissolved in a solvent and developer are widely used. In the recording material, the color former reacts with the developer to form a colored image.
The recording material can be a pressure sensitive material or a heat sensitive material. With pressure sensitive material, the microcapsules containing the color former are ruptured by application of pressure to form a color image through the reaction of the color former with the developer. The pressure sensitive recording material includes carbonless copy paper recording material wherein a color former layer comprising microcapsules containing a color former and a developer layer containing the developer are respectively formed on surfaces of separate supports or separate surfaces of one support and are in contact with each other to be used; and self-coloring pressure sensitive recording material (e.g., pressing-type paper or self-contained paper) comprising a self-coloring layer having both the color former and the developer provided on one side surface of a support.
The carbonless copy paper recording material generally includes an upper paper having a color former layer provided on one side surface of a support (which usually is a sheet of paper) that is generally referred to as a CB sheet, an intermediate paper having a color former layer provided on one side surface of a support and a developer layer on another side surface of the support that is generally referred to as a CFB sheet, and a lower paper having a developer layer provided on one side surface of a support that is generally referred to as a CF sheet. The intermediate paper is usually used in the form of two or more sheets. Such carbonless copy paper recording material is employed by bringing the color former into contact with the developer by rupturing the microcapsules by pressure to form a color image.
In the self-coloring pressure sensitive recording material, when pressure is applied to a surface having a self-coloring layer, microcapsules in the layer are ruptured to form a color image on the self-coloring layer through the reaction of the color former with the developer. Therefore, the material is usually employed for writing or drawing an image such as a letter on a paper placed on the self-coloring layer with writing instruments or a typewriter, for directly printing a colored image on the self-coloring layer with a printer or a typewriter, or for printing a letter for OCR (optical character reader) on the self-coloring layer.
In preparation of plural copies, a self-coloring pressure sensitive recording material using an upper paper having a self-coloring layer provided on one side surface of a support and a color former layer on another side surface of the support, in combination with an intermediate paper having a color former layer and developer layer and a lower paper having a developer layer is occasionally employed. The types of the self-coloring layer of the self-coloring pressure sensitive recording material include a layer composed of two layers consisting of a color former layer containing microcapsules containing a color former and a developer layer containing a developer which are superposed upon each other, and a single layer consisting of one layer containing a color former and a developer.
The heat sensitive recording materials containing microcapsules, for example, are those having a heat sensitive layer which contains microcapsules containing a color former and a developer, as described in the literature such as in Japanese Patent Provisional Publication No. 63(1988)-265682 and No. 1(1989)-105782. Such recording material has the advantages that it can be designed for OHP (over head projector) or multicolor type.
The microcapsules, which are contained in the above recording materials, contain a color former dissolved in a solvent. It is necessary that such solvent is capable of dissolving the color former. Examples of the solvents generally include kerosene, paraffin, naphthene oil, alkylated biphenyl, alkylated terphenyl, chlorinated paraffin, alkylated naphthalene, diaryl alkane and phthalic acid ester. Some of these solvents generally give off noxious odors and some may be harmful so that environmental pollution can occur.
Over the years, the art has developed a number of color formers which are readily dissolved in various solvents with the resulting solutions formulated into microcapsules for recording material. For instance, published European Patent Application No. 629511 discloses a recording material containing both microcapsules containing an electron-donating color former dissolved in a solvent and an electron-accepting developer. The solvent comprises a glyceride and the electron-donating color former comprises a fluoran compound of the formula: ##STR1##
wherein R.sup.1 represents an alkyl group of 1 to 4 carbon atoms, R.sup.2 represents a branched alkyl group of 4 to 12 carbon atoms or a tetrahydrofurfuryl group, and each of R.sup.3 and R.sup.4 independently represents a hydrogen atom, a halogen atom or a methyl group, provided that R.sup.1 differs from R.sup.2.
Published PCT Application No. WO 95/07187 describes an internal phase solution for a coating of rupturable microcapsules for application to a base sheet to form a pressure-sensitive record material. The solution comprises one or more color formers of which at least 90% are monoamino and/or diamino fluoran derivatives dissolved in a solvent comprising 80% to 100% of one or more vegetable and/or animal oils. The color formers preferably comprise only monoamino and/or diamino fluoran derivatives and the solvent comprises only one or more vegetable and/or animal oils. Dissolution of the color formers in the solvent may take place at a temperature in the range 100.degree. C. to 135.degree. C. and microcapsules containing such a color former solution may be formed by conventional coacervation processes below 70.degree. C. Disclosed illustrative color formers are
2'-(octylamino)-6'-(diethylamino) fluoran, PA1 2'-anilino-3'-methyl-6'-(diethylamino) fluoran, PA1 6'-(diethylamino)-2'-(1,1-dimethylethyl) fluoran, and PA1 6'-(dibutylamino)-3'-methyl-2'-(phenylamino)-spiro[isobenzofuran-1(3H),9'-[ 9H]xanthen]-3-one.
U.S. Pat. No. 4,837,210 describes certain chromogenic dialkyl-substituted aniline fluoran compounds which can be used as color formers in recording materials. The compounds are disclosed as being initially substantially colorless, but produce gray-black colored products on reaction with certain acidic developer materials. In the background of the patent, other U.S. patents are noted including U.S. Pat. No. 4,226,912 which relates to a heat-sensitive recording material containing a chromogenic material which is composed of at least 60% by weight of two or more kinds of black color developing fluoran compounds. Published European Patent Application No. 672,730 discloses mixtures of color formers including fluoran color formers in pellet form which are useful in pressure sensitive and heat sensitive recording material. It has also been reported that a 1:1 mixture of 3-diethylamino-6-methyl-7-(2',4'-dimethylanilino)fluoran and 3-dibutylamino-6-methyl-7-anilinofluoran has been used to attain better solubility in a composition that is encapsulated and used in a recording material.
Despite various advances, the art has continued to seek color formers that can be dissolved at higher concentrations and/or can be dissolved in safer and/or less expensive solvents.